[Diy_efi] Are Jeep CPU's Reprogrammable?

[Van Setten, Tim @ ACSSD]

One of my neighbors recently purchased a 2005 Jeep Rubicon which has been a
bit of a disappointment in terms of off-road gas consumption and
transmission controllability.
Does anybody know if it can be reprogrammed as in the shift points of the
tranny?  Maybe a few engine tweaks as well?
Someone else mentioned that you can always "Chip" it, but from what I
remember, there is no chip to change.  Just a data port.

Anyone with any experience with who and what can be done?  Thanks.....Tim.